Chromaffin cells and their derivatives contain and release several neuroactive substances, including catecholamines and opioid peptides. The transplantation of chromaffin cells into CNS pain modulatory regions sensitive to these agents may provide a permanent and locally available source of neuroactive substances for the relief of pain. The goal of the proposed program is to assess the potential for neural transplants to provide a new therapeutic approach to the problem of intractable pain. Transplant tissue for these studies will include rat adrenal medullary tissue, isolated bovine chromaffin cells, PC12 cells, and derivatives of these using pharmacological and molecular manipulations. These graft tissues will be placed in the midbrain periaqueductal gray or the dorsal spinal cord, and behavioral, biochemical, and morphological changes will be monitored over time. To assess the potential for therapeutic use, both acute and chronic pain models will be used. Pharamacological studies will include responses to cell surface receptor agonists and antagonists, as well as the role of released catecholamines and opioid peptides from transplanted cells. In addition, enkephalinase inhibitors may prolong alterations in pain sensitivity. Tolerance and tachphylaxis will also be assessed. Biochemical levels of neuroactive substances may be altered when cells are transplanted to the new CNS environment. Biochemical changes in host and grant tissue will be determined using radioimmunoassays and HPLC. Furthermore, in the new CNS environment, transplanted cells may differentiate morphologically, and form synaptic or non-synaptic relationships with the host CNS. Host-graft relationship will be studied morphologically using electron microscopy and immunocytochemistry. Both biochemical and morphological changes may be induced by environmental manipulation with agents such as nerve growth factor or butyric acid. Effects of these agents on host and graft tissue will also be determined. In addition, it may be possible to increase the level of opioid peptide production in cells using molecular manipulations. A goal of this proposal is to develop a cell line for transplantation that will produce increased levels of opoid peptides using gene transfer techniques.